Apparatus and method of providing an initiation voltage to a rechargeable battery system

ABSTRACT

An undervoltage recovery pulse network (500) and method used with a lithium ion battery system (400) for providing a initiation voltage to a battery controller (503) which has been operationally disabled due to an event associated with the lithium ion battery system (400). The undervoltage recovery pulse network (500) includes a switch (523) for detecting a first voltage applied to a data terminal (537) by a charging system. A coupler (525) is used for supplying a second voltage from a charging terminal (535) to the battery controller (503) to enable the battery controller from its disabled state. The battery controller (503) then connects the voltage potential of a cell (501) to the charging terminal (535) for detection by a charging system. This allows the charging system to detect an attached battery so it may apply a charging voltage to charging terminal (535).

TECHNICAL FIELD

This invention relates in general to battery recharging and moreparticularly to systems for rechargeable battery cells.

BACKGROUND

An increasing number of portable electronic products are available todaywhich operate on a battery source within the device. These productsinclude such things as cellular telephones, portable radios, pagers andvoice recorders which are conveniently mobile and operate usingrechargeable batteries. Many different battery chemistries have beenused for many years which meet the need for recharging capability.Probably the most popular chemistries include nickel cadmium and nickelmetal hydride. A relatively new chemistry, however, generally referredto as lithium ion, enables a cell to be recharged while offering manyadvantages over other types of rechargeable cells. These benefitsprimarily are directed to low weight and overall size with a high energydensity. One unique factor to be considered when using, a lithium ioncell is its charging scheme. A lithium ion cell is not charged in thesame manner as cells utilizing a nickel chemistry.

Nickel-cadmium and nickel metal hydride cells are typically chargedusing a rapid charge by applying a constant current until a certainevent occurs. This event may be coupled to the cell reaching apredetermined high voltage, decreasing to a predetermined low voltage oran increase in the cell's temperature. This is in contrast with thelithium ion cell which requires a two step charging process to achieveoptimum performance. The first step of this process provides that thebattery charger apply a constant current level while the cell's voltageremains below a predetermined threshold. Once the voltage increases tothat threshold, the second step insures the battery charger is held atthe threshold voltage allowing the current to decrease. Once the currentdecreases sufficiently to a desired level, the lithium ion cell is fullyrecharged.

This two step process presents a problem when considering charginglithium ion cells in a charger designed for nickel systems. Generally,nickel system chargers apply only a constant current which allows thevoltage of the cells to rise unimpeded. The voltage may rise to anylevel provided the battery does not become too hot, i.e. increase to aundesired and dangerous level. Once the nickel system battery becomeshot, the charger detects this state and switches from the rapid highcurrent charge to a value of approximately 5-10% that of the rapidcurrent value. This lower current mode is generally referred to as atrickle current or trickle charge.

Hence, the charging scheme offered by current nickel system chargerswill not properly charge a lithium ion cell. Should a lithium ion cellbe placed or forced in to the nickel system charger the result could bepotentially dangerous since the lithium ion cell could quickly overheat.Therefore, the need exists for a battery charging circuit or systemwhich can be retrofitted to the control circuitry of an existing lithiumion cell allowing the cell to safely use a nickel system charger.

In addition to supplying a retrofitable circuit allowing lithium ionbatteries to be recharged using nickel system chargers, a completebattery system would also be useful which would supply additionalsystems to insure safety when recharging a lithium ion cell in this way.

Still yet another problem associated with utilizing a lithium ion cellwith a nickel system charger occurs when circuitry, which is part of thebattery system, has disconnected the lithium ion cell from the chargingterminals used to charge the cell. The event may occur to due highcurrent or voltage conditions and, due to no operating voltage beingavailable, will leave many of the control and safety systems associatedwith the battery without power. Thus, no power is present at thecharging terminals of the battery.

There are two ways in which a nickel based battery charging systemtypically detects when to charge an attached battery. These includedetection of a thermistor and/or a voltage on the battery. Many chargingsystems in current use apply a very brief pulse when a data line isdetected upon initial connection of the battery to the charging network.Although this pulse is enough to enable or wake up the batterycontroller, this remains ineffective. Therefore, one method which hasbeen used to provide a start-up or initiation voltage to the internalsystem to restore voltage to the charging contacts is so called the"double insertion method." This involves actually disconnecting thebattery from the charging system once inserted and then reconnecting itat second time. The battery must be reconnected twice since by the timethe battery controller is actuated, and the battery controller allowsthe cell voltage to be applied to the charging contacts, the chargersystem has already made a determination that no battery is connected.Hence, the battery remains connected to the charging system without anyannunciation by the charging system, the consumer understands this tomean that the battery is dead when in fact it is merely disabled.However, once the battery is disconnected and then reconnected, thecharger recognizes a voltage potential on the charging terminals sincethe battery controller was restarted with the first voltage or pulse.

The "double insertion method" is burdensome and confusing requiringconnection and reconnection of a disabled battery before recharging canbegin. Therefore, the need exists to provide a device and method whichallows a charging system to enable a battery controller within adisabled lithium ion battery without the inconvenience of having toconnect, disconnect and reconnect the battery to the charging system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing operation of the high temperaturesimulator in accordance with the invention.

FIG. 2 is a partial schematic diagram in accordance with a preferredembodiment of the invention showing a high temperature simulator whichis used when a high current source is available.

FIG. 3 is a partial schematic diagram in accordance with a preferredembodiment of the invention showing a high temperature simulator whichis used when only a low current source is available.

FIG. 4 is a partial schematic diagram in accordance with a preferredembodiment of the invention showing an alternative embodiment of a hightemperature simulator to that shown in FIG. 2.

FIG. 5 is a block diagram showing operation of a retrofitable chargingand safety system used with a lithium ion cell in accordance with theinvention.

FIG. 6 is a partial schematic diagram showing an undervoltage recoverypulse network in accordance with the preferred embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a block diagram depicting operation of a hightemperature simulator for a rechargeable battery system which cansimulate a high battery temperature condition is shown. The rechargeablebattery may typically be one based on a lithium ion chemistry, lithiumpolymer chemistry or lead acid chemistry. The high temperature simulatorallows a rechargeable battery to be charged using an alien chargingsystem or charging network which generally has an incompatible chargingscheme. An alien charging system may be one used with a nickel cadmiumor nickel metal hydride type cells and has a first mode of operation andsecond mode of operation. The first mode of operation is generally aquick or fast mode while the second mode is a slower or trickle chargemode. These charging systems are generally referred to as nickel systembattery chargers and are configured to charge nickel metal hydride ornickel cadmium cells.

As will be described in greater detail below, the preferred embodimentof the invention takes advantage of an inherent feature present with anickel system battery charger. This feature insures that rapid chargingof a rechargeable battery ceases when the appropriate controlinformation is received from the battery. This control information isrelated to the battery's temperature during rapid charge. When thepredetermined temperature is reached, the nickel system battery chargerautomatically switches to a low current or trickle charge state wherethe rechargeable battery can be charged more slowly.

A preferred embodiment of the invention shows battery 100 which includesa rechargeable cell 101. As indicated above, rechargeable cell 101 maybe one or more cells with a lithium ion chemistry or the like. A controlcircuit 103 measures or observes the voltage of the rechargeable cell101 while under charge by charging system 105. Charging system 105 istypically a charger used for nickel cadmium or nickel metal hydridecells. Control circuit 103 may be a comparator circuit or the like suchas Motorola Integrated Circuit Model No. SC371013F/FER. Once controlcircuit 103 determines a predetermined voltage level or voltagepotential has been reached, control circuit 103 produces a controlsignal on control line 106. The predetermined voltage is generally aselected voltage limit which is determined by the operational voltage ofthe rechargeable cell 101 and may depend on specific cell chemistryand/or associated charging algorithm.

The control line 106 is used to convey the control signal from controlcircuit 103 to each of low voltage switch 104, high voltage switch 107and a temperature simulator device such as thermistor switch 111. Lowvoltage switch is used to disconnect rechargeable cell 101 in the eventits voltage becomes too low, and thereby preventing damage to the cell.High voltage switch 107 and a delay circuit 109 are positioned in serieswith charging system 105 and are used to provide an open circuit after adesired delay period when a predetermined voltage is reached duringcharging. The delay period is used to allow charging system 105 to reactto changes in current through temperature sensor or thermistor 113.Without the delay, charging system 105 may interpret the opening of highvoltage switch 107 as rechargeable cell 101 being disconnected. Oncethis occurs, charging system 105 may turn itself off.

Thermistor switch 111 is attached to control circuit 103 and is alsotriggered by the control signal through control line 106 to provide ashort circuit to thermistor 113. As is well known in the art, theresistive value or state of thermistor 113 changes in response totemperature changes of rechargeable cell 101. Thus, the current flowingthrough thermistor 113 changes in relation to the ambient environment inwhich thermistor 113 is exposed. This current flow is interpreted by thecharging system 105 as a temperature value which it uses to determinewhen to switch charging modes. These modes are typically switched from afast or rapid charge state, where charging rate is at a high level to aslower charge state where the charging rate is reduced. Thermistorswitch 111 is attached to thermistor 113 and is controlled by controlcircuit 103. When actuated, thermistor switch 111 alters the currentflow or state of thermistor 113. As indicated above, this increase incurrent through thermistor 113 is detected by charging system 105 as ahigh temperature condition. Thus, thermistor switch 111 acts as acontrol circuit to change the operational state of thermistor 113.Thermistor switch 111 then simulates a high temperature state ofrechargeable cell 101. In response thereto, charging system 105 switchesfrom a high rapid or substantially fast charge mode to a slow, low ortrickle charge mode. Since rechargeable cell 101 was first allowed tocharge to its predetermined voltage i.e. the first step of its chargingscheme, the trickle charge mode now allows rechargeable cell 101 to becharged in accordance with the second step of its charging scheme. Oncecharging system 105 has switched to the lower current, the voltages ofrechargeable cell 101 will drop slightly from their previous level dueto internal resistance present within rechargeable cell 101. This lowerlevel of current allows continued charging of the rechargeable cellwhile its voltage is below the threshold voltage level, until the cellbecomes fully charged. However, charging using charging system 105 willgenerally take longer than if the ideal lithium ion charging regime wereused.

FIG. 2 illustrates a schematic representation of the high temperaturesimulator circuit 201 typically used in a rechargeable battery 200 wherecontrol circuit 209 can sink sufficient current to an isolated orvirtual ground. As is seen in FIG. 2, rechargeable battery 200 typicallyincludes a charging voltage node 203, a temperature node 205 and avirtual ground node 207. In operation, a charging voltage is connectedto the charging voltage node 203 and virtual ground node 207. A batterycharging system (not shown) measures temperature through temperaturenode 205 to determine when to change or switch operating modes. Thebattery charging system may be one designed for nickel cadmium cells,nickel metal hydride cells or the like. As indicated above, low voltageswitch 210 is used to prevent rechargeable cells 211 from dischargingbelow a selected value. Conversely, when control circuit 209 detectsthat rechargeable cell 212 has reached a predetermined high voltageduring charging, it sends a control signal through control line 211 tohigh temperature simulator circuit 201 and high voltage switch 217through delay 214. High temperature simulator circuit 201 is comprisedof a diode 213 and resistor 215. When the control signal enables hightemperature simulator circuit 201 and high voltage switch 217, itswitches the voltage at temperature node 205 from a high level tovirtual ground node 207. This has the affect of pulling or lowering thevoltage on temperature node 205 to a low value since current is beingsunk to virtual ground node 207. Thus, this lower voltage simulates ahigh temperature condition of thermistor 216. This is detected by thebattery charging system on temperature node 205 as high temperaturecondition which enables it to switch modes. Although diode 213 could beused alone, resistor 215 is used to insure the voltage on temperaturenode 205 is not dropped to too low a value since certain varieties ofbattery chargers enter a test mode under these conditions.

FIG. 3 illustrates a schematic representation of the high temperaturesimulator circuit 301 typically used in a rechargeable battery 300 suchas a lithium ion battery. High temperature simulator circuit 301 is usedwhere control circuit 315 cannot sink a significant amount current toallow the circuit shown in FIG. 2 to be used. It should be evident tothose skilled in the art the function and operation of the rechargeablecells 304, low voltage switch 306 and delay 308 are like that describedin FIGS. 1 and 2 above. Rechargeable battery 300 utilizes a chargingnode 302, temperature node 303 and virtual ground node 305. The hightemperature simulator circuit 301 is comprised of an N-channel MOSFET307, resistor 309, resistor 310, P-channel MOSFET 311 and resistor 313.In operation, when control circuit 315 actuates high voltage switch 317,this biases the gate-source junction of P-channel MOSFET 311. Resistor313 is used to pull up or increase the voltage on the gate of N-channelMOSFET 307 if control circuit 315 should fail. Resistor 313 is of asufficiently high resistance to allow only a negligible current flowthrough it from charging node 302 when a control signal is enabled fromcontrol circuit 315. This causes P-channel MOSFET 311 to become a lowresistance value and current flows through P-channel MOSFET 311,resistor 309 and resistor 310. The resulting voltage produced alsobiases N-channel MOSFET 307 into a low resistance state switching it toan on state. Once N-channel MOSFET 307 is switched on, resistor 316 actsto drop voltage on temperature node 303 sufficiently to indicate orsimulate to a battery charging system (not shown) that a hightemperature condition exists. The voltage at temperature node 303 isdropped low since the current passing through this node is directed orsunk to virtual ground node 305. Thus, the voltage measured acrossthermistor 314 is simulated using high temperature simulator circuit301. The configuration shown in FIG. 3 may only be used if controlcircuit 315 cannot handle excessive current it must sink from anattached charging system. The circuit shown in FIG. 3 is more complexhowever it has the advantage of low current since only a negligibleamount of current flow through resistor 313 when a control signal isenabled from control circuit 315.

FIG. 4 illustrates a schematic representation of a high temperaturesimulator circuit 320. High temperature simulator circuit 320 is analternative embodiment to that shown in FIG. 2 where a high currentsource from an attached charging system is available. It should beevident to those skilled in the art the function and operation of therechargeable cells 322, low voltage switch 324, high voltage switch 326and delay 328 are like that described in FIGS. 1, 2 and 3 above. In thepreferred embodiment, high temperature simulator circuit 320 includes aninverter gate 321, P-channel MOSFET 323 and resister 325. In operation,like the other embodiments above, when control circuit 327 detects ahigh voltage condition in cells 329, a control signal is emitted oncontrol line 331. This pulls or lowers the voltage on control line 331to a low state which also controls the input of inverter gate 321 low.This biases P-channel MOSFET 323 turning it on. When P-channel MOSFET isturned on this pulls or lowers the temperature node 333 to a low statesince temperature node 333 is effectively connected to virtual groundnode 335. The value of resister 325 is used to control and/or select thedesired temperature level that is interpreted by an attached batterycharging system. Thus, an attached battery charging system which isconnected to temperature node 333 detects a high temperature in view ofthe low voltage on this node. High temperature simulator circuit 320acts to simulate or create a false high temperature condition.

The preferred method of practicing the invention includes charging arechargeable battery with a charging apparatus having a first mode ofoperation and second mode of operation whose charging scheme isincompatible with the rechargeable cell within said rechargeablebattery. The steps include applying a charging current from the chargingapparatus to the rechargeable cell. Detecting a voltage potential of therechargeable cell. Measuring the temperature of the rechargeable cellusing a temperature sensor and sending a control signal from a firstcontrol network to a second control network when a predetermined voltagepotential is reached to allow the temperature sensor to simulate a hightemperature to the charging apparatus. Finally, sensing a simulated hightemperature of the charging apparatus to change from said first mode ofoperation to the second mode of operation allowing the rechargeable cellto charge at a slower rate.

Thus, hot battery simulator apparatus and method disclosed will enable anew generation of lithium cell chemistries to be used without the burdenof the consumer having to purchase a special charger to accommodate andrecharge these rechargeable cells such as lithium ion cells. This willmore greatly enhance the benefits and advantages of utilizing lithiumbased cells keeping overall cost low as opposed to buying a completelynew charger and batteries for any desired application.

FIG. 5 shows a block diagram of a lithium ion battery safety and controlcircuit platform or battery system 400. This system has been developedfor use in future lithium ion batteries, as well as a retrofit forbatteries currently in use. The system is intended to accommodatevarious user and manufacture recommendations for providing a useful andsafe rechargeable battery system that can be charged with an existingcharger designed only for nickel battery systems.

The battery system 400 for use with a portable electronic deviceincludes protection circuitry for one of more cells 401. Cells 401 aregenerally lithium ion or the like and provide a voltage potential atoperating terminals 403 and 411. Operating terminals 403, 411 are usedto supply an operating voltage to a portable product (not shown) whichuses battery system 400 for a power source. The system further includescharging terminals 405, 407 which are used to receive a charging voltagewhich is applied to recharge cells 401. A data terminal 409 suppliesinformation to a charging system from a memory 412. Memory 412 is a ROMtype memory or the like and conveys information to those types ofchargers known as "smart chargers". This information is relating to thebattery type and charging regime which a charging system would berequire to know before recharging the battery. Finally, a temperatureterminal 413 is used to allow the charging system to detect thetemperature of the battery during recharging. This is accomplishedthrough the use of a thermistor 415 or like device which permitsmeasurement by the charging system of an accurate battery temperatureduring the recharging process. A thermistor control 417 is attached tothermistor 415 and is controlled by primary overvoltage control 419 andsecondary overvoltage control circuit 421 to change or redirect thecurrent flow around thermistor 415. Thermistor control 417 is discussedin more detail above and has the effect of simulating a high temperaturecondition of cells 401. This is subsequently detected by an attachedcharging system (not shown) allowing it alter its charging mode ofoperation from a fast charge to a slower or trickle charge.

Primary overvoltage control 419 is connected with cells 401 and is usedto measure the cumulative voltage present on the cells 401 to preventthe cells from increasing or rising above a selected voltage. In theevent primary overvoltage control 419 fails or becomes inoperative,secondary overvoltage control 421 is used to measure the voltage on eachindividual cell and prevent each individual cell from increasing orrising above a selected voltage. Upon actuation of either primaryovervoltage control 419 or secondary overvoltage control 421, a controlsignal is supplied to one or more independent overvoltage switches 423.Actuation of any one of independent overvoltage switches 423 provides anopen circuit which disconnects cells 401 from operating terminals 403,411. Each control signal is delayed using a delay 425 or delay 427respectively which delays the control signal before actuating any ofindependent overvoltage switches 423. The delay 425, 427 is used toinsure thermistor control 417 receives its control signal beforeindependent overvoltage switches 423 are enabled which would disconnectthe charge current from cells 401. This allows an attached chargingsystem to detect simulated changes in the temperature of cells 401 andalter its mode of operation before actuating any of independentovervoltage switches 423. Similarly, undervoltage control 428 is used tomeasure the cumulative voltage of the cells 401 and provides a controlsignal to undervoltage switch 429 when the cumulative voltage dropsbelow a predetermined level. Like independent overvoltage switches 423,undervoltage switch 429 is connected serially with cells 401 anddisconnects cells 401 when the voltage of the cells drops to anundesirably low level to prevent damage to cells 401.

Cell balancing control 422 is comprised a load (not shown) connected inparallel with each of cells 401. Cell balancing control 422 acts toswitch the load across a cell in order to maintain each of the cells atapproximately the same voltage level during charging. The load is usedto slightly discharge a single cell in the event the cell becomes aslightly higher voltage as compared with other cells. The load isdisconnected once the cell voltage has been reduced to a levelcompatible with other cells.

Primary short circuit protector 431 is used to measure the voltageacross both independent overvoltage switches 423 and undervoltage switch429. Since these switches inherently have a stable DC resistance, thevoltage across them is proportion to the current which runs through themwhen cells 401 are being recharged. When the current through independentovervoltage switches 423 and undervoltage switch 429 reaches apredetermined, i.e., excessive level, this also drops the voltage acrossthese switches. In response to a selected voltage drop acrossindependent overvoltage switches 423 and undervoltage switch 429,primary short circuit protector 431 provides a control signal toundervoltage switch 429. This insures the undervoltage switch 429disconnects cells 401 from terminals 403-411 to prevents any furtherdischarge until the excessive high current conditions removed. This actsas a safety feature to prevent cells 401 from generating excessive heatand possible damage under extremely high load conditions.

Overcharge current protector 433 is a complement to primary shortcircuit protector 431 by directly measuring the amount of currentthrough it. If the current reaches a selected level, a control signal isgenerated by overcharge current protector 433 to independent overvoltageswitches 423 which disconnects cells 401 from terminals 403-411.Additionally, overcharge current protector 433 is used to limit thecharge current. Since cells 401 is a lithium ion type cell and is usedwith a charger designed with a charging regimen for nickel chemistrycells, it often may charge at a current level higher than at the optimumlevel for a lithium ion cell. In this case, overcharge current protector433 will detect this high current level and provide a control signal tothermistor control 417 to simulate a high temperature condition. Thistricks the nickel system charger and forces it into a low current ortrickle charge mode which is more suited for the lithium ion cell.

Electronic device overvoltage protector 435 is connected serially withcells 401 and charging terminal 405 and is used to determine when any ofindependent overvoltage switches 423 have been actuated. Since actuationof these switches may cause the voltage of cells 401 to increase or riseto a level which could damage electronic equipment attached to thebattery system 400 at operating; terminals 403, 411 electronic deviceovervoltage protector 435 detects actuation of independent overvoltageswitches 423 and in response thereto, disconnects operating terminal403, from charging terminal 405 to prevent an attached charger fromsupplying a potentially damaging voltage to an electronic deviceattached to operating terminal 403. Alternatively, if electronic deviceovervoltage protector 435 is not used, a thermal fuse 437 can beimplemented. Thermal fuse 437 is also attached serially between cells401 and charging terminal 405 and is generally a high power zener diode(not shown) or the like. The zener diode acts to shunt current whencells 401 are above a selected voltage since this would likey damage anelectronic device attached to operating terminal 403.

A secondary short circuit protector 439 acts as a current detectionelement and is also connected in series between cells 401 and operatingterminal 403 and charging terminal 405. Secondary short circuitprotector 439 may be a polyswitch or the like and is used to detectexcessive current which may not be detected by either primary shortcircuit protector 431 or overcharge current protector 433.

Finally, a current fuse 441 also acts as a current detection element andis placed in series between cells 401 and operating terminal 403 andcharging terminal 405 and is used as a last resort or ultimate backup inthe event of a catastrophic failure in which current rises to anunacceptable level. The fuse is generally located close to cells 401 tominimize runner length. The current fuse 441 is preferably a slow actingtype so as not to interfere with other current protection systems withlithium ion battery system 400.

Finally, undervoltage recovery pulse network 500 is used in the eventthat any one of independent overvoltage switches 423 have been actuatedand cells 401 are no longer connected to charging terminal 405. Underthese conditions, when the battery is initially connected to a chargingsystem (not shown), the charging system first detects a voltage presenton charging terminals 405, 407. If no voltage is present, the chargingsystem determines that no battery is connected to it and does notprovide a charging voltage to operating terminals 403, 411. When thebattery is initially connected however, an initial pulse of apredetermined voltage and amplitude is supplied from the charging systemto data terminal 409. This pulse is detected by undervoltage recoverypulse network 500 which utilizes the voltage to restore operation ofindependent overvoltage switches 423. Once operation of independentovervoltage switches 423 is restored, the appropriate switch is closedwhich restores continuity between cells 401 and charging terminal 405through electronic device overvoltage protractor 435. Thus, the voltageof cells 401 is restored in a time fast enough that a charging systemwill detect this voltage on operating terminals 403, 411 even when abattery system 400 is disabled, and cells 401 disconnected due to someevent which has occurred. The charging system will recognize the voltageon charging terminals 405, 407 and begin a charging cycle by applying acharging voltage to these terminals.

FIG. 6 shows a schematic diagram of the undervoltage recovery pulsenetwork 500 as used in a typical lithium ion rechargeable batterysystem. As noted in FIG. 5 the system includes among other things, aplurality of cells 501, a battery controller 503, overvoltage switches505, undervoltage switch 507, comparator 509, thermistor 511 andthermistor control 513. A electronic device overvoltage protector 515 iscomprised of transistors 516, 518 and 520 for monitoring the state ofsaid overvoltage switches 505 to prevent an electronic device attachedto cells 501 from being damaged.

The undervoltage recovery pulse network 500 is comprised of transistors523 and 525 along with resistors 527, 529, 531, 533 and capacitor 532.Assuming the battery has experienced and event in which either primaryovervoltage switch 505 or secondary overvoltage switch 506 are actuatedor undervoltage switch 507 has been actuated, Cells 501 are no longerconnected to charging terminals 535. If a battery, including cells 501,were connected to a charging network, no voltage would be detected bythe charging network to start a charging cycle.

In order to prevent this undervoltage recover pulse network 500 acts inthe following manner. When the portable battery is initially attached toa charging network, a low level voltage or pulse is generally applied toeither data terminal 537 or thermistor terminal 539 if the chargingnetwork is so equipped. Since thermistor terminal 539 is connected tocharging terminal 535 through diode 541, a small voltage is typicallyalready present on charging terminal 535. Assuming the voltage ispresent on data terminal 537, it is directed to a voltage dividercomprised of resistors 529, 531. This results in transistor 523 andtransistor 525 being switched on which supplies the voltage fromelectronic device terminal 536 to charging terminal 535. At some latertime, the charging network applies a detection pulse to chargingterminal 535 in order to detect a voltage potential of a connected cell.The detection pulse enables a current to pass from charging terminal 535to electronic device terminal 536 through transistor 523 which passesthrough cells 501. This has the result of enabling the comparator 509which turns on primary overvoltage switch 505 comprised of a transistor.Thus, transistor 523 provides a temporary bypass for electronic deviceovervoltage protector 515 for allowing a start up pulse or initiatingvoltage to reactivate the battery controller 503. Electronic deviceovervoltage protector 515 includes a transistor 516 which couples orbypasses a charging voltage on charging terminal 535 through transistor518 and transistor 520 to secondary overvoltage switch 506 and batterycontroller 503. This occurs even when cells 501 are not connected tocharging terminals 535. Once battery controller 503 is reactivated,transistor 542 is turned on by a voltage divider comprised of resistor543, 544 when voltage reaches approximately 3.0 volts. This allowsnormal operation of thermistor 511. Transistor 523 is an N-channelMOSFET and switches to an off state when the voltage at electronicdevice terminal 536 reaches a voltage greater than on data terminal 537i.e. approximately 5.0 volts. Resister 531 and capacitor 532 provide apulse coupled path for those charges which do not have data terminal 537but do provide some type of output pulse such a charge outputcapacitance. Once the voltage is detected on charging terminal 535, allother battery systems beginning normal operation.

While the preferred embodiments of the invention have been illustratedand described, it will be dear that the invention is not so limited.Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as defined by theappended claims.

What is claimed is:
 1. A device used with a rechargeable battery forproviding a initiation voltage to a battery controller which has beenoperationally disabled due to an event associated with said rechargeablebattery, said rechargeable battery charged by a charging system andincluding at least one cell, a charging terminal for supplying acharging current to said rechargeable battery and a data terminal forsupplying information to said charging system, said device comprising:atleast one switch for detecting a first voltage applied to said dataterminal by said charging system; a coupling means for supplying asecond voltage from said charging terminal to said battery controller toenable said battery controller; and wherein a battery controller directssaid voltage potential of said at least one cell to said chargingterminal for detection by said charging system.
 2. A device as in claim1 wherein said data terminal is used to send charging information tosaid charging system.
 3. A device as in claim 1 wherein said dataterminal is used to send temperature information to said chargingsystem.
 4. A device as in claim 1 wherein said at least one cell is alithium ion cell.
 5. A device as in claim 1 wherein said chargingterminal supplies a charging voltage from said charging system to saidat least one cell.
 6. A device as in claim 1 wherein said coupling meansis comprised of a plurality of transistors.
 7. A method of enabling abattery controller which has been disabled due to a safety controlsystem associated with a portable battery, said portable batteryincluding a charging node for supplying a charging current to at leastone cell within said portable battery and a data node for conveyinginformation to a charging system, comprising the steps of:attaching saidportable battery to said charging system; detecting a first voltageprovided at said data node by said charging system; actuating a firstswitch with said first voltage from said data node; enabling saidbattery controller with a second voltage provided by said chargingsystem through said charging node; and connecting said at least one cellto said charging node for detection by said charging system.
 8. A methodas in claim 7 wherein said enabling step further comprises the stepof:actuating a second switch with said battery controller which connectssaid at least one cell with said charging node.
 9. A method as in claim7 wherein said information is charging information relating to said atleast one cell.
 10. A method as in claim 7 wherein said information istemperature information relating to said at least one cell.
 11. Anundervoltage pulse generator circuit for allowing a battery controllerwhich controls at least one switch establishing continuity between abattery cell and a charging terminal to be reactivated by a batterycharger when it has been temporarily disabled due to an event associatedwith said battery cell, said undervoltage pulse generator circuitcomprising:a first switch for receiving a pulse provided by a dataterminal on said battery charger and connecting a charging terminal to aelectronic device supply terminal in response thereto; a second switchconnected to said first switch and said battery controller for providinga path for a current applied to said charging terminal by said batterycharger to said battery controller; and wherein said battery controlleris reactivated by said current applied to said charging terminalreestablishing continuity between said battery cell and said chargingterminal for detection by said battery charger.
 12. An undervoltagepulse generator circuit as in claim 11 wherein said battery cell has alithium ion chemistry.
 13. An undervoltage pulse generator circuit as inclaim 11 wherein said battery charger is used for nickel metal hydridecells.
 14. An undervoltage pulse generator circuit as in claim 11wherein said first switch is an N-channel MOSFET.
 15. An undervoltagepulse generator circuit as in claim 11 wherein said second switch is anN-channel MOSFET.
 16. An undervoltage pulse generator circuit as inclaim 11 wherein said data terminal is used to convey charginginformation to said battery charger.
 17. An undervoltage pulse generatorcircuit as in claim 11 wherein said data terminal is used to conveytemperature information of said battery cell to said battery charger.18. A method of enabling a control system used with a portable batterywhich has been inactivated by a control switch on the portable batterycomprising the steps of:receiving a pulse at a first node on saidportable battery used to convey data to a battery charging system;activating a bypass switch with said pulse to connect a voltage suppliedat a second node of said portable battery, by said battery chargingsystem, to reactivate said control system; and opening said controlswitch to connect said portable battery to said second node fordetection by said battery charging system.
 19. A method of enabling acontrol system as in claim 18 wherein said battery is a lithium ionbattery.
 20. A method of enabling a control system as in claim 18wherein said first node is used to convey charging information from saidportable battery to said charging system.
 21. A method of enabling acontrol system as in claim as in claim 20 wherein said second node isused to supply a charging voltage to said portable battery.
 22. A methodof enabling a control system as in claim 18 wherein said first node isused to convey temperature information from said portable battery tosaid charging system.
 23. A method of enabling a control system as inclaim 18 wherein said second node is used to supply a charging currentto said portable battery.
 24. A method of enabling a control system asin claim 18 wherein said bypass switch includes at least one transistorconnected serially with said portable battery and said second node.